Electrode lets lithium batteries charge in just two minutes

Researchers craft an electrode that combines a lot of surface area with a high …

Batteries are an essential part of most modern gadgets, and their role is expected to expand as they're incorporated into vehicles and the electric grid itself. But batteries can't move charge as quickly as some competing devices like supercapacitors, and their performance tends to degrade significantly with time. That has sent lots of materials science types into the lab, trying to find ways to push back these limits, sometimes with notable success. Over the weekend, there was another report on a technology that enables fast battery charging. The good news is that it uses a completely different approach and technology than the previous effort, and can work with both lithium- and nickel-based batteries.

The previous work was lithium-specific, and focused on one limit to a battery's recharge rate: how quickly the lithium ions could move within the battery material. By providing greater access to the electrodes, the authors allowed more ions to quickly exchange charge, resulting in a battery with a prodigious charging rate. The researchers increased lithium's transport within the battery by changing the structure of the battery's primary material, LiFePO4.

The new work also gets fast charges, but by a rather different route. The authors, from the University of Illinois, don't focus on the speed of the lithium ions in the battery; instead, they attempt to reduce the distance the ions have to travel before reaching an electrode. As they point out, the time involved in lithium diffusion increases with the square of the distance travelled, so cutting that down can have a very dramatic effect. To reduce this distance, they focus on creating a carefully structured cathode.

The process by which they do this is fairly simple, and lends itself to mass production. They started with a collection of spherical polystyrene pellets. By adjusting the size of these pellets (they used 1.8µm and 466nm pellets), they could adjust the spacing of the electrode features. Once the spheres were packed in place, a layer of opal (a form of silica) was formed on top of them, locking the pattern in place with a more robust material. After that, a layer of nickel was electrodeposited on the opal, which was then etched away. The porosity of the nickel layer was then increased using electropolishing.

When the process was done, the porosity—a measure of the empty space in the structure—was about 94 percent, just below the theoretical limit of 96 percent. The authors were left with a nickel wire mesh that was mostly empty space.

Into these voids went the battery material, either nickel-metal hydride (NiMH) or a lithium-treated manganese dioxide. The arrangement provides three major advantages, according to the authors: an electrolyte pore network that enables rapid ion transport, a short diffusion distance for the ions to meet the electrodes, and an electrode with high electron conductivity. All of these make for a battery that acts a lot like a supercapacitor when it comes to charge/discharge rates.

With the NiMH battery material, the electrodes could deliver 75 percent of the normal capacity of the battery in 2.7 seconds; it only took 20 seconds to recharge it to 90 percent of its capacity, and these values were stable for 100 charge/discharge cycles. The lithium material didn't work quite as well, but was still impressive. At high rates of discharge, it could handle 75 percent of its normal capacity, and still stored a third of its regular capacity when discharged at over a thousand times the normal rate.

A full-scale lithium battery made with the electrode could be charged to 75 percent within a minute, and hit 90 percent within two minutes.

There are a few nice features of this work. As the authors noted, the electrodes are created using techniques that can scale to mass production, and the electrodes themselves could work with a variety of battery materials, such as the lithium and nickel used here. It may also be possible to merge them with the LiFePO4 used in the earlier work. A fully integrated system, with materials designed to work specifically with these electrodes, could increase their performance even further.

Of course, that ultimately pushes us up against the issue of supplying sufficient current in the short time frames needed to charge the battery this fast. It might work great for a small battery, like a cell phone, but could create challenges if we're looking to create a fast-charge electric car.

That's really cool from a practical "no need to sit on a charger overnight, just toss it on for a few seconds and you're good" perspective, I'm a bit worried about being able to discharge a battery that quickly. What happens when the thing is inevitably shorted thanks to damage or poor manufacturing somewhere? Explosion? Instant slag?

Current laptop "explosions" are misnomers, but this could make it real.

I've always figured the goal charge time for electric cars should roughly equal what we live with today. If it takes 2 minutes to completely fill my tank with gas, then it should take 2 minutes to bring my car's battery to 100%. 2 seconds is nice, but if it can reduce safety hazards, I think everyone would be happy with 2 minutes. This is some very exciting progress!

Well, a standard household socket can deliver 15 amps, so with your laptop or cell phone battery size you should be able to calculate just how long it would take to charge if you could dump the whole line in there. Most smartphones are in the 800-1500 mAh range.

so if the cathode was in the shape of a porous mesh, how did they construct an anode? typically batteries use large flat plates or spiral cylinders, in which case the anode and cathode can simply be mirrored, but the inverse of a porous mesh is a bunch of disconnected spheres. or does the hydride in NiMH (and similar for the analog in LiOn) act as its own anode as it fills in the mesh?

i wanted to say matrix instead of mesh (i think it's more accurate) but that damn movie kept popping into my head.

Are current charge rates limited by the standard household output? If not, just how much faster can you make a charge rate before it is meaningless for regular use?

No, the Chevy Volt and the Nissan Leaf both use 3.3kW chargers (roughly 220V/15A). The largest practical household current would be 15.4kW or 220V/70A (for a 100A service, common for about the last 40-50 years I think).

A battery like the Volt (16kWh, ~9kWh usable) would recharge in under 35 minutes, while the Leaf's battery would recharge in 75 minutes (24kWh, ~19kWh usable).

Batteries are all about give and take. Recharging faster is always possible, but at some cost, usually lower capacity and a shorter usable lifespan. The converse is true, the slower you charge/discharge the battery the longer it will retain its capacity. A host of other factors also matter - battery temperature, chemical composition, etc.

For most people who will drive plug-in cars (and still own another gasoline powered car) they'll charge overnight or while at work, so they wont be looking to get the fastest charge possible, they just want it ready to go by 7AM or whatever time they leave for work. This allows the car's brain and the power company (through smart metering) to work together to reduce strain on the grid and the car's battery.

I've always figured the goal charge time for electric cars should roughly equal what we live with today. If it takes 2 minutes to completely fill my tank with gas, then it should take 2 minutes to bring my car's battery to 100%.

My house has electricity, why would I want to stop at a service station to fill up?

An hour or two to charge would be just fine generally, although 5 minutes would be most excellent for those times you run low then suddenly have to use the car. Let's hope this really is easily manufactured.

I'm a bit worried about being able to discharge a battery that quickly. What happens when the thing is inevitably shorted thanks to damage or poor manufacturing somewhere?

IIRC, LiFePO4 batteries are "safe chemistry" which is why they almost never come with a protection circuit. They can withstand temperatures in the hundreds of degrees before run-away reactions occur. The laptop battery fires are caused by LiCo batteries, shoddy manufacturing, and no/malfunctioning protection circuit.

Lets say I make a Huge gigantic version of this - as one earlier poster stated - it can charge quickly - but how quickly? Could I take a lighting strike to a battery farm of this design and charge the field in a split second?

I'm a bit worried about being able to discharge a battery that quickly. What happens when the thing is inevitably shorted thanks to damage or poor manufacturing somewhere?

IIRC, LiFePO4 batteries are "safe chemistry" which is why they almost never come with a protection circuit. They can withstand temperatures in the hundreds of degrees before run-away reactions occur. The laptop battery fires are caused by LiCo batteries, shoddy manufacturing, and no/malfunctioning protection circuit.

Agreed the battery material might well be fairly safe, but what about where the current is going? If you have a couple of 2000mAH AA cells, when you do the math, and consider the amperage you get if you discharge the entire thing in 3 Seconds.. I think you could practically do spot welding with that kinda current

I can remember when someone in our electronics class found some discarded gates gel-cells that were 2AH 2.2v and about the size of a D cell with two tabs on top. They were tarpotted into this giant circle about 18-24" in diameter, had obviously had been subjected to a rather catastrophic discharge considering most of the insulation was melted off the wiring that connected them. But after careful trickle charging, most of them were good. You could drop a paper-clip, a beefy one, across the terminals of a single cell and in about one second it was orange, a second later yellow, a second after that nearly white and then just melted poof..

Pretty darned scary the amps they would put out, and I'm sure those things had no-where near the discharge rate that we're talking about for the batteries above. No, we are talking here about something with discharge rates that could easily slag stuff, much less starting fires.

so if the cathode was in the shape of a porous mesh, how did they construct an anode? typically batteries use large flat plates or spiral cylinders, in which case the anode and cathode can simply be mirrored, but the inverse of a porous mesh is a bunch of disconnected spheres.

No. It could be a connected series of tubes, like the internet.

Think sponge. It's a mesh of fiber yet water can penetrate into all the negative spaces. If that sponge was in a bowl and had a stand-off from the bottom of the bowl, then the sponge could be the cathode, and the water could be connected to an anode on the bottom of the bowl because the sponge and bowl never come in contact.

Did they talk about efficient and subsequently heat output? Seems like a fire hazard.

I thought this too, but after some thinking (and someone correct me if I'm wrong) but I think batteries get so hot because of the resistance to taking a charge at such a fast rate. This technology makes it sounds like the large surface area reduces that resistance allowing to charge that fast without burning up.

Also, the article states they got almost 1000 cycles so obviously they would have noticed it going off in a blaze of glory if it reacted how previously we would have expected.

The Nintendo DS Lite battery is 2 Amp-Hours. That means it can deliver 2 amps (2 coulombs per second) for 1 hour, or 1 amp for 2 hours, or whatever, at the battery's voltage of 1.65V. If you want to transfer that much charge in 2 minutes, you need 60 amps at whatever the battery charging voltage is.

I might be wrong about this, but it's pretty difficult to for ordinary electronics to withstand that many amps without catching fire.

Does anybody know "battery charging voltage"? What is it typically (as compared to battery voltage)?

This would make a world of difference for laptop batteries. Sure, some people are indeed away from power for eight hours at a time but most of us could live with a one minute charge every two or three hours.

Let's see how much power I'd need to charge a laptop in, say, one minute.

My laptop has a 11.1 volt three cell battery with a capacity of 5,200 mAh. That's fairly typical.

We convert to minutes: 312,000 milliamp-minutes. That's 312 amp-minutes, so we'll add on 20% charging inefficiency to make 374 amps for one minute.

We have 62 amps at ~12 volts lost in charging inefficiency and being converted to heat in the battery. That's 744 watts. The battery would instantly explode, violently.

So, too, would something else. That power has to come from somewhere, the battery's charging circuit inside the laptop. These are typically 90% efficient, so we'll add on 10% of the input current lost in the laptop, making a drain from external supply of 411 amps. This time, 37 amps are lost in the charge controller, but at a much higher voltage, typically 19V. That's 710 watts.

We're almost at 1.5 KILOWATTS inside a laptop. That laptop is going to be on fire and exploding.

So what do we power it with? The only option is a wall charger, which has to source 411 amps at 19V (this is 7.8 kilowatts) but they're usually only 85% efficient and much worse when dealing with very large currents, which this certainly is. From the wall, the charger is pulling 8,980 watts. and losing 1.1 kilowatts as heat.

The charger and laptop combined are losing 2.6 kilowatts as heat. Sit and get your head around that a moment. That's a LOT of heat. It's enough to raise the laptop's temperature to several thousand degrees over the course of the minute's charge.

Phones don't have it that much better. Let's say we're using the standard single cell 1 Ah battery and we want to charge it in a minute, to which we need 60 amps at around 4.5 volts going into the battery. The battery itself is heating up at a rate of 360 watts while the phone is heating at the rate of 300 watts. The SMPS power supply, which has to source around 85 amps at five volts (425 watts) is creating around 85 watts of heat itself. The conductors needed to safely handle 85 amps are, simply put, girders. Forget all pretensions of a flexible cable from the charger to the phone!

We have over six hundred watts in the space of a phone. There's not a portable cooling solution on the planet able to keep up with that, it has the thermal density of a nuclear reactor core.

You know how many articles about new battery technology I've seen over the years? Bazillions. You know how fast battery technology moves ahead? As fast as a speeding snail.

Seriously? In 1999 there was no way something as powerful as the iPad 2 could run for hours and hours and hours on such a small battery. The batteries we have today are remarkable; it's just that we forget how remarkable they are every time a new gadget ships that uses them to their fullest capacity.

Taking the example above, it's 5.2 amp-hours. That's 5.2 amps for one hour to fully discharge (assuming a full charge). So to charge in two minutes, it would be 5.2 * 30 or 156 amps. You're never going to get any wiring that can handle that kind of amperage.

It's time at this point to pick a new goal (our original target of two minutes was infeasible). Let's say one that gives a maximum current of 20A. If we pick 15 minutes (which is very much faster than current laptop batteries charge), it gives 5.2 * 4 or 20.8 amps which is reasonable.

How much power do we need? Well we need 20.8 amps at 11 volts plus 20% inefficiency, so it's 20.8 * 11 * 1.2 = 275W charger is needed. This type of power supply is usually used to supply power to desktop computers. It would be expensive but not ridiculously so. This gives a draw of 275 / 120 = 2.3 amps at the 120V wall socket which is not too much.

So now we have a laptop that only needs to be plugged in for 15min. Which is great cause you're not tethered to the wall, but the brick now weighs as much as the laptop and the cable is as thick as a regular extension cord. That would be fine if there was such a thing as a standard plug and voltage for laptops, then the trendy hipster coffee shop would have plugs at each table and they could charge you $3 if you're not getting the coffee to go (to pay for all the electricity)

If you are pumping gas a 0.5 l/second (which is about how fast the dials turn, IIRC), you are charging your car at 17.4 MEGAWATTS. Big power stations don't get much above 1000 MW, for comparison. Most renewable plants making headlines are about 1 MW.

Yes, petrol engines can be as bad as 20% efficient. If your electric car was 100%, you'd only need one-fifth the energy, but that's still 2 megawatts. Big numbers.

A large factory consuming a megawatt of power needs to contact the electricity companies when they start up or shut down. If they have a failure and go out unexpectedly, power failures occur as the grid tries to adjust. We cannot have Joe Blow on the forecourt switch in out a 2MW charger! So large buffer banks will be needed at any charging locations, and these will need power supplies at the level of a major transmission line.